IS12 Introduction to Programming Lecture 13: Conditionals

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IS12 - Introduction to Programming Lecture 13
Conditionals

• Peter Brusilovsky
• http//www2.sis.pitt.edu/peterb/0012-041/

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Course Logistics

• We are at a turning point
• We have got through C basics and programs are
  getting complicated
• Are you able to follow?
• How challenging was the exam?
• Can you understand and write programs?
• This is the last chance to catch up

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What you have to do?

• Attend lectures and browse it again
• Do your reading assignments
• Explore all examples - run, modify...
• Solve all problems (including exercises)
• Work with KnowledgeTree - quizzes, dissections,
  Expression Executor
• Try free C tutorials (KnowledgeSea)
• Ask questions in the forums
• Come and talk with us, use office hours

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Outline

• If and If-else
• The use of if-else
• The use of if
• Simple nested ifs
• If inside a loop
• Conditional operator
• If-else vs. conditional operator

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Conditional Statement if-else

• if (expression)
• statement-1
• else
• statement-2
• nextstatement
• If expression is not 0 (true) - statement-1
• If expression is 0 (false) - statement-2
• In any case after that - nextstatement

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Flowchart of if-else
Expression ?
! 0 (true)
0 (false)
Statement-1
Statement-2
Nextstatement
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if-else with blocks

• if (expression)
• statement-11
• ...
• else
• statement-21
• nextstatement

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Conditional Statement if

• if (expression)
• statement-1
• nextstatement
• If expression value isnt 0 (true) - statement-1,
  after that - nextstatement
• If expression value is 0 (false) - nextstatement

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Flowchart of if
Expression ?
! 0 (true)
0 (false)
Statement1
Statement3
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if with blocks

• if (expression)
• statement-11
• ...
• nextstatement

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Example Maximum with if-else

• include ltstdio.hgt
• void main()
• int a, b
• printf("Enter two integers ")
• scanf("d d", a, b)
• printf("Maximum of d and d ", a, b)
• if(a lt b)
• printf("is d\n", b)
• else
• printf("is d\n", a)

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Example Maximum with if

• include ltstdio.hgt
• void main()
• int a, b, max
• printf("Enter two integers ")
• scanf("d d", a, b)
• max a / pre-assignment /
• if(a lt b)
• max b / re-assignment /
• printf("Maximum of d and d is d", a, b, max)

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Example Variable Rate (1)

• define THRESHOLD 5000
• include ltstdio.hgt
• void main()
• float rate1, rate2, interest_rate / interest
  rates /
• float capital / capital /
• float annual_interest / annual interest /
• / read data /
• printf("Interest rates (xx.xx) ")
• scanf("f f", rate1, rate2)
• printf("Capital (.cc) ")
• scanf("f",capital)

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Example Variable Rate (2)

• / calculate the rate /
• if (capital lt THRESHOLD)
• interest_rate rate1
• else
• interest_rate rate2
• printf("The rate for .2f is .2f\n",
• capital, interest_rate)
• / calculate capital /
• annual_interest capital interest_rate / 100
• printf("Interest 6.2f New capital 9.2f\n",
  annual_interest, capital annual_interest)

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Example Nested if - max3

• include ltstdio.hgt
• void main()
• int a, b, c
• printf("Enter three integers ")
• scanf("d d d", a, b, c)
• printf("Maximum of d, d and d is ", a, b, c)
• if(a gt b)
• if(a gt c)
• printf("d\n", a)
• else
• printf("d\n", c)
• else
• if(b gt c)
• printf("d\n", b)
• else
• printf("d\n", c)

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Example Running Max

• define SENTINEL -1
• include ltstdio.hgt
• void main ()
• int max, nextnumber
• printf("Number ")
• scanf("d", nextnumber) / read first number
  /
• max nextnumber / pre-assignment /
• while (nextnumber ! SENTINEL)
• if (max lt nextnumber)
• max nextnumber
• printf("Number ")
• scanf("d", nextnumber)
• printf ("Max d\n", max)

The Running Max pattern Interleaved with The
Sentinel Loop pattern
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Conditional Operator

• Expr1 ? Expr2 Expr3
• Conditional operator calculates the value from 3
  arguments (expressions)
• First, Expr1 is evaluated
• If it is true (not zero), then Expr2 is
  calculated its value is the result
• If it is false (zero), then Expr3 is calculated
  its value is the result

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Conditional Operator Examples

• min a lt b ? a b
• rate capital lt 3000 ? rate1 rate 2
• printf("c\n", (lower ? 'a' 'A'))
• x a (b 2 ? b - 1 b)

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Compare Conditionals

• Conditional statement
• Controls the order of statement execution
• if (capital lt THRESHOLD)
• interest_rate rate1
• else
• interest_rate rate2
• Conditional operator
• Calculates a value
• interest_rate capital lt THRESHOLD ? rate1
  rate2

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Before next lecture

• Do reading assignment
• Perry Chapter 11 Chapter 13 Hello Conditional
• Run Classroom Examples
• Exercises variable rate in a loop calculating
  minimum of a sequence
• Check yourself by working with KnowledgeTree and
  its components